Rewrite the equation by completing the square. $x^{2}+4x-21 = 0$ $(x + $
Explanation: Begin by moving the constant term to the right side of the equation. $x^2 + 4x = 21$ We complete the square by taking half of the coefficient of our $x$ term, squaring it, and adding it to both sides of the equation. Since the coefficient of our $x$ term is $4$, half of it would be $2$, and squaring it gives us ${4}$. $x^2 + 4x { + 4} = 21 { + 4}$ We can now rewrite the left side of the equation as a squared term. $( x + 2 )^2 = 25$